In large off the road tires, such as are used in construction or agriculture, the treads are formed of large tread elements often described as lugs or bars. In the manufacture of such tires the outside diameter or peripheral surface of the tread often times is not uniform within a circumferential plane relative to the distance as measured from the tire's axis of rotation. Assuming a tire was mounted onto a rim and the rim was perfectly centered on an axis of rotation, then a perfectly molded tire should have a constant radial distance measured from the axis to any location on the outer peripheral surface within any circumferential plane perpendicular to the tires axis. Unfortunately, the method of manufacturing tires results in many non-uniformities such that the radial distance from a tread elements outer surface can vary widely. In large tires this condition is commonly referred to as radial runout. Radial Runout creates a first harmonic vibration as the tire rotates. This results in harsh lug impacts that vibrate the vehicle and the driver. Correcting this problem can dramatically eliminate almost all of the first harmonic vibrations.
In U.S. Pat. No. 6,237,402 the problem was addressed by finding a high spot on the tire and then shifting a rim disk relative to the rim toward the location of the maximum radial runout by a distance half the amount, thereby minimizing the amount of runout. This prior art method while being a great field expedient did not truly correct the tires condition but simply masked the problem. The tires runout conditions are not limited to one high spot and one low spot across the entire tread width. In U.S. Pat. No. 6,237,402 the equatorial center plane in the crown of the tire was the only circumferential plane measured. The movement of the rim disk quite frankly could only address one worst-case condition at a time. Accordingly the best that could be achieved was a minimizing of the problem.
In a more complex analysis of the tires tread profile it is well known that variations in the tire profile can occur anywhere between the tread shoulders. Accordingly the tires entire lateral profile should be considered when looking for radial runout conditions.
Wada, et al in U.S. Pat. No. 5,485,406 describes an apparatus and a method for detecting the tread profile of a tire mounted about an X axis comprising a non contact Y detection means movable parallel to the X axis for measuring the distance at a right angle between such means and the peripheral surface of the tread. The method is applied to the measurement of a profile of a tire when the X and Y data are divided into groups for the crown and shoulder portions of the tire respectively. The method also includes computation of radial runout of the tire using regular rotation position data output corresponding to particular X and Y values for rotation of the tire.
While Wada appreciates the problem of measuring a test tire for the profile of the tread, this has little useful value if corrective measures are not taken. In small tires such as passenger or light truck tires subtle design changes can be made to minimize runout. In some cases tires can be force grinded to take down high spots.
In large tires such as agricultural tires the use of force grinding can be used, however, the appearance is usually very noticeable. Secondarily, the amount of material that needs to be grinded is substantially larger than is commonly required in smaller tires. This can be time consuming but more importantly the rubber dust created in grinding operations requires more sophisticated material handling and removal systems.
It is an object of the present invention to provide a reliable way to inspect a tire, even a large agricultural or off-road tire, for radial runout.
It is a further object of the present invention to correct for the runout condition in a fast and reliable manner while minimizing the amount of tread rubber that is required to be removed.
It is a further object of the invention to provide a like new polished rubber finish on the tire after correcting for radial runout.